UNIVERSITY OF GAZIANTEP FACULTY OF ENGINEERING

CIVIL DEPARTMENT

CE-547

Corrosion of Plain &Reinforced concrete

Report # 3:

(Concrete damage due to corrosion of

reinforcement )

Submitted to:Doç.Dr. Mehmet GESOĞLU

Prepared by:Chalak Ahmed Mohammed

chalak.mohammed@gmail.com

2014 45056

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Date : 17.03. 2015

Corrosion of reinforcing steel is a major deterioration process affecting reinforced concrete structures worldwide. Corrosion causes cracking and spalling of the concrete cover, loss of load bearing capacity and ultimately structural collapse.

Fig.(1)

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Cracking of the cover is often a critical limit state and this can be modelled as a two-stage process consisting of an initiation phase, defined as the time taken for corrosion to commence, and a propagation phase, where the formation of corrosion products induces expansive stresses and damage. Until recently, most research has focused on the time up to corrosion initiation, while the propagation phase leading to failure remains poorly understood. One important aspect that lacks understanding is the amount of corrosion products that must form to cause damage. It is likely that not all corrosion products contribute to cracking because some are soluble species that dissolve in the pore solution and migrate into adjacent cement paste away from the sites of corrosion.

Fig.(2)

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Observations

Corrosion products can migrate through the aggregate-paste interface as well as the ‘bulk’ paste. They can be deposited in cracks, air voids, inner & outer hydration products, and relicts of reacted slag. A distinct boundary between the affected and unaffected paste can be seen, indicating the extent of the rust penetration (Fig 3).

Fig 3: BSE montage of samples with different degrees of corrosion, showing rust accumulating at the steel-concrete interface and migrating into the cement paste, cracks and air voids

EDX microanalyses show that the affected paste has higher analysis totals, and Fe and O contents, but is depleted in Ca (Fig 4

Subsequent corrosion products are forced to accumulate at the steel-concrete interface, inducing expansive pressure that leads to bond failure and cracking.

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Fig 4: BSE images and EDX element maps indicating the extent of rust penetration and decalcification.

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Image analysis found that only a small amount of corrosion product, approximately 100μm thick covering about 20% of the rebar perimeter, is needed to generate the first visible cover crack (~0.05mm width). Once cracking has initiated, the rust preferentially deposits in large cracks rather than pore spaces in the cement paste. Hence, the extent of rust penetration into the cement paste does not increase much with corrosion (Fig 5b).

Fig 5: Effect of corrosion degree on the amount of damage and area of the rust layer (CL) and rust penetrated paste (RP).

Regards...

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